From: Oleg Nesterov <oleg@redhat.com>
To: Alexey Gladkov <gladkov.alexey@gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Vasiliy Kulikov <segoon@openwall.com>,
Al Viro <viro@zeniv.linux.org.uk>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Pavel Emelyanov <xemul@parallels.com>,
James Bottomley <James.Bottomley@HansenPartnership.com>,
"Dmitry V. Levin" <ldv@altlinux.org>
Subject: Re: [RFC] Add option to mount only a pids subset
Date: Thu, 23 Mar 2017 17:05:07 +0100 [thread overview]
Message-ID: <20170323160507.GA23135@redhat.com> (raw)
In-Reply-To: <20170320125855.GG4554@comp-core-i7-2640m-0182e6>
Again, I can't really review this, I know nothing about vfs, but since
nobody else replied...
On 03/20, Alexey Gladkov wrote:
>
> @@ -97,7 +169,23 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
> ns = task_active_pid_ns(current);
> }
>
> - return mount_ns(fs_type, flags, data, ns, ns->user_ns, proc_fill_super);
> + root = mount_ns(fs_type, flags, data, ns, ns->user_ns, proc_fill_super);
> +
> + if (!IS_ERR(root)) {
> + if (!proc_fill_options(data, &opts))
> + return ERR_PTR(-EINVAL);
So we have to call proc_fill_options() twice, not good... Yes, I understand
why, but perhaps we factor it out somehow, we can pack options + pid_ns into
sb->s_fs_info. Nevermind, this is minor.
> + if (opts.pid_only) {
> + int ret;
> +
> + if (!ns->pidfs && (ret = fill_pidfs_root(root->d_sb)))
> + return ERR_PTR(ret);
> +
> + root = ns->pidfs;
Afaics this lacks dget(ns->pidfs) which should pair with dput(mnt.mnt_root)
in cleanup_mnt(). IIUC otherwise ns->pidfs can go away after umount, OTOH,
if we return ns->pidfs then dget(sb->s_root) in mount_ns() is not balanced.
But this all is fixeable.
So with this change "mount -opidonly" creates another IS_ROOT() dentry which
is not equal to sb->s_root. I simply do not know if this is technically
correct or not... but, say, the "Only bind mounts can have disconnected paths"
comment in path_connected() makes me worry ;)
And this obviously means that /path-to-pidonly-mnt/ won't share dentries with
the normal /proc mount. Not really good imo even if not really wrong... Lets
look at proc_flush_task(). The exiting task will flush its $pid dentries in
/proc/ but not in /path-to-pidonly-mnt/ iiuc. Again, not really a bug, but
still...
Oleg.
next prev parent reply other threads:[~2017-03-23 16:07 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-18 22:53 [PATCH] Add pidfs filesystem Alexey Gladkov
2017-02-18 23:34 ` kbuild test robot
2017-02-18 23:34 ` kbuild test robot
2017-02-20 4:05 ` Eric W. Biederman
2017-02-20 10:36 ` Alexey Gladkov
2017-02-22 20:11 ` Richard Weinberger
2017-02-21 14:57 ` Oleg Nesterov
2017-02-22 7:40 ` Pavel Emelyanov
2017-02-22 12:04 ` Alexey Gladkov
2017-02-22 13:08 ` Pavel Emelyanov
2017-02-22 11:53 ` Alexey Gladkov
2017-02-22 15:37 ` Dmitry V. Levin
2017-02-22 17:48 ` Oleg Nesterov
2017-02-22 19:56 ` Alexey Gladkov
2017-03-06 23:05 ` [RFC] Add option to mount only a pids subset Alexey Gladkov
2017-03-07 16:24 ` Andy Lutomirski
2017-03-09 11:26 ` Djalal Harouni
2017-03-09 20:52 ` Eric W. Biederman
2017-03-11 21:51 ` Alexey Gladkov
2017-03-11 0:05 ` Alexey Gladkov
2017-03-07 17:49 ` Oleg Nesterov
2017-03-10 23:46 ` Alexey Gladkov
2017-03-12 1:54 ` Al Viro
2017-03-12 2:13 ` Al Viro
2017-03-13 3:19 ` Andy Lutomirski
2017-03-13 13:27 ` Al Viro
2017-03-13 15:24 ` Andy Lutomirski
2017-03-23 15:59 ` [PATCH] proc: allow to change proc mount options per mount Djalal Harouni
2017-03-20 12:58 ` [RFC] Add option to mount only a pids subset Alexey Gladkov
2017-03-23 16:05 ` Oleg Nesterov [this message]
2017-03-23 22:57 ` Alexey Gladkov
2017-03-23 16:06 ` Djalal Harouni
2017-03-23 22:07 ` Alexey Gladkov
2017-03-26 7:03 ` Djalal Harouni
2017-03-30 21:45 ` Alexey Gladkov
2017-02-27 18:56 ` [PATCH] Add pidfs filesystem Michael Kerrisk
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